An Internet Protocol (IP) Multimedia Subsystem (IP Multimedia subsystem, IMS) service has become a main orientation for mobile development and is currently capable of coupling a call in a Circuit Switched, CS, domain to an IMS side to implement a cross-network connection between the CS domain and an IMS domain.
However, a seamless transfer of a speech channel cannot be implemented currently due to the limited switching capability in the CS domain. For example, if the battery of a mobile phone runs out when the user of the mobile phone in the CS domain is in a call, it is expected to transfer the call to another terminal, or in a case in which another call transfer needs to be performed, a cross-network seamless transfer of a speech channel cannot be performed without affecting a calling party's call, thereby causing great inconvenience for user's usage.